The mixing of air with smoke in a tobacco product has been utilized for many years to produce a milder smoking product. The first air diluted smoking product was probably made by the smoker. For instance, for many years cigar smokers have manually pierced holes in the cigar wrapper leaf prior to lighting the cigar in order to permit air to be drawn into the body of the cigar during smoking. This air dilution produced a milder smoke. When the cigarette was first developed, there was no need for air dilution because cigarette smoke was much milder than the cigar smoke. As time passed, however, smokers tended to prefer milder smoking cigarettes.
Various methods have been used to produce milder smoking cigarettes; for example, toasting the tobacco, utilizing filters of different materials, such as paper, cellulose acetate, charcoal, etc., tobacco and filter additives and tobacco substitutes. Nevertheless, the most widely used and important method of producing a milder cigarette is air dilution. Initially, the cigarette paper (tobacco rod wrapper) itself was perforated to introduce air into the tobacco rod during smoking similarly to piercing the cigar wrapper leaf. Again, this was initially done manually by the smoker. Later, the cigarette paper was perforated prior to applying it to the tobacco rod, either through mechanical perforating means or electrostatic perforating means. Electrostatic perforating was preferred since the holes were microscopic in size and, therefore, invisible. Another method of introducing air into the tobacco rod was through the use of "porous" paper. A special paper making process is used to produce a uniform porosity in the cigarette paper by forming microscopic pores or openings in the paper to permit the passage of air.
As the smoker's preference continues to change, further efforts are being made to produce a milder smoking cigarette and to reduce the particulate matter and nicotine in the smoke. Filtration of the smoke utilizing various types of filter material and filter configurations in conjunction with air dilution has become the preferred method of reducing particulate matter and nicotine in the cigarette smoke. Air dilution is normally accomplished in two ways. First, by admixing the air and smoke within the filter element and, secondly, by preventing the admixing of the air and smoke until they reach the smoker's mouth. The primary filtration material used today is cellulose acetate fibers which are formed into cylindrical rods. The most widely used air dilution system is to admix the air and smoke within the filter prior to entering the smoker's mouth.
Numerous kinds of filter devices have been developed to permit admixing of air and smoke within the filter. The most prominent method is to form a filter plug making a rod of cellulose acetate fibers and wrapped in a "porous" plugwrap. The filter plug is then attached to a tobacco rod by a tipping paper which has a series of mechanical perforated holes. Another method which has been developed utilizes a porous tipping paper rather than a perforated tipping paper over the filter plug having a porous plugwrap.
The porous plugwrap is usually wrapped around the cellulose acetate rod and glued along a longitudinal edge; therefore, there is only a single longitudinal strip of adhesive along the edge to prevent the passage of air into the cellulose acetate rod. The filter plugs are attached to the tobacco rod by the tipping paper and use various gluing techniques to prevent the adhesive from covering the entire tipping paper, which would prevent the passage of air.
U.S. Pat. No. 3,805,800, for example, discloses one method of applying a wet glue pattern to a porous tipping paper. As can be seen, a checker-board pattern, circumferential strips, or longitudinal lines of glue can be used so that large areas of the tipping paper remain free of adhesive to insure a sufficient amount of air can pass into the filter.
U.S. Pat. No. 4,035,220 discloses a method which is called "laking". In this method, a wet glue is applied to the tipping and, because of the phenomena called "laking," which occurs when two objects which are not totally wetted are adhered together, the adhesive forms beads or collects in small defined areas, thus, producing void areas through which air can be drawn.
It can be readily seen, in either of these patents, that the tipping has large areas void of adhesive and, thus, the porosity of the tipping can be maintained at a selected level. Should either of these methods be used, an additional gluing step is required to insure that the adhesive-free edge of the tipping gear is glued down. If this edge is not glued down, the air dilution of each product can vary and the uniformity of air dilution which is required cannot be obtained.
Another problem results when using a wet adhesive and porous tipping together. Porous tipping must be very thin to obtain the desired porosity. Because of this thinness, the tensil strength of the paper is low, and there is a tendency for the paper to break under production conditions. When the porous tipping is wetted with an adhesive, the tensil strength is further reduced and breakages occur more frequently, particularly if the pattern of adhesive is transverse to the direction of movement of the tipping paper. Also, when using a wet adhesive on a porous paper, there is a tendency for the glue to bleed through the pores in the paper so that glue gets on the outside of the filter paper which is not acceptable from an appearance standpoint; and, also, if the glue gets on the outside of the filter paper, it is transferred to the machine parts where it builds up and reduces the efficiency of the machine.
Because of the numerous problems which occur when using porous tipping, most air ventilated cigarettes use tipping which has been perforated by mechanical means (i.e., needles). Although mechanically perforated tipping is the most widely used, it does have some drawbacks. One drawback is the size of the holes. No matter what type of mechanical device is used, the holes formed are macroscopic in size and can be seen. From a marketing point of view, this is undesirable. For this reason, most of the air diluted cigarettes utilize a white tipping paper which has been mechanically perforated. If mechanically perforated imitation cork tipping is used, the perforations can easily be seen because of the contrast produced by the white plugwrap being exposed through the holes. Thus, if imitation cork tipping is to be used, it is preferable to have microscopic holes which cannot be seen.
Although microscopic holes can be made electrostatically and this method has been used in the tobacco industry for many years in cigarette paper, it has been only recently that electrostatically perforated tipping has been developed to such an extent where it might possibly be used on tipping paper. There were a number of reasons for the slow development of the electrostatic perforated tipping; for example, the thickness of the tipping paper required that more voltage be used which produces scorching of the paper, thus, making the machine design more difficult. Also, there was great difficulty in controlling the location and size of the holes. As can be easily understood, the size and number of holes must be controlled within a given range or the porosity of the tipping will vary too greatly to give the uniformity of air dilution which is required. Furthermore, locating the holes in a specific area (i.e., circumferential band) is important because of the gluing requirement. Although recent developments in electrostatically perforating techniques have overcome some of the problems with respect to size, number and location of holes, other problems must be overcome before electrostatically perforated tipping paper could efficiently be used on a tobacco product.
For example, the principal problem with electrostatically perforation is the width of the circumferential bands of perforations which must be used to insure the proper porosity of the paper. Using presently known gluing techniques, a substantial portion of the edge of the tipping must remain unglued, thus, providing a possibility of non-uniform air dilution between products. The only known way to overcome this problem at the present time is to add a gluing device to the machine which will glue the edge down.
There also exists some device in which a heat-activatable adhesive can be used on the tipping paper. The heat-activatable adhesive is pre-coated on the tipping prior to being used on the filter cigarette assembly machine. A device such as the one disclosed in U.S. Pat. No. 3,420,243 to McArthur can be used to attach the pre-coated tipping to the cigarettes. However, the basic problem encountered with the wet glue techniques would also be encountered with the heat-activatable adhesive.
Because of these difficulties, there exists a need for a ventilated tipping paper in which the porosity can be controlled and the tipping would adhere to the filter plug without leaving wide gaps along its edge. There also exists a need for a method of making such tipping paper which can be used with either white or imitation cork tipping.